Clinical Research- The overall focus of this center is stroke prevention in a defined population. The aim of this research is the identification of stroke in the population and the determination of the factors that affect the occurrence of stroke. A randomized clinical trial will assess the effect of carotid endarterectomy compared to a small dose of aspirin on the occurrence of stroke in persons with carotid artery stenosis. A case-control population based study will estimate the independent risk of stroke for hypertension and cardiovascular risks and the prevalence of those risk factors over the time from 1960-1984. The incidence of stroke in Rochester from 1985-1989 will be assessed to determine whether a further increase has occurred. The risk of stroke from mitral valve prolapse and from mitral and aortic valvular heart disease will be estimated each with a population based inception cohort and follow-up through the medical record. The incidence rate of dementia subsequent to stroke in Rochester will be estimated and the cumulative probability of the development of dementia following cerebral infarction will be estimated.